PISIDIUM. 
269 
and with two or three deep sulcatlons, forming 
darker zones across the shell ; margin of the 
valves meeting at a rather acute angle ; umbones 
obtuse, and not much produced, sometimes 
slightly capped, as in (7. cdlyculata; cardinal 
teeth rather prominent; lateral moderate and 
thin. (t. 12. f. 152.) 
Cyclas cinerea. Hanley^ Hecent Shells.^ i. 90. t. 14. f. 44. — 
Pisidium cinereum. Alder^ Cat Supp. 4. ; Forbes and Han« 
ley^ B. M. ii. 125. t. 36. f. 2. — Cardium cajertanum. Poli^ 
Sicil. i. 65. t. 16. f. 1. — Pisidium cajertanum. Bourg. Voy. 
Mer, Mart 80.; Moq. Tand, Moll. Franc, ii. 584. t. 52. 
f. 16— 32.— Pisidium australe. Philip. Sicil. i. 39. — Cyclas 
lenticulare. Norm, Cycl. 8. t. 8. f. 7, 8. — P. lenticulare, 
Dup. B[. M. 681. t. 30. f. 2. — P. tetragonum. Norm, 
Cycl. 5. — P. thermale, P. normandianum, P. Iratianum, 
P. Gassierianum, and P. calyculatum. Dupuy^ Cat. — P. 
limosum. Gass. Moll. Agen, 206. t. 2. f. 10, 11. 
Distorted: P. sinuatum. Bourg. Jour. Conch. 1851, 421., 
1852, 49. t. 1. f. 6—10. 
Yar., more ventricose, and produced at the umbones. 
Inhab. ponds. North of England. 
Animal white ; siphonal tube very short, broad, 
and flat, truncated at the end, and seldom protruded 
much beyond the edge of the shell. 
This species may generally be readily distinguished 
from others of the genus by its more compressed and 
oval form, and its cinereous colour. It is the largest 
of the minute species. (^Alder,) 
Length 2-lOths, height 7-40ths, thickness 5“40ths 
of an inch. 
The genus Cyrena is now no longer found alive 
in this country, but it must have lived here at no very 
great period of time (geologically considered), for it 
is found an abundant fossil at Grays, in company 
